1. Field of the Invention
The present invention relates to an alumina particle, a method of manufacturing the alumina particle, a resin composition, and a method of manufacturing the resin composition.
2. Description of the Related Art
To improve properties of materials such as rigidity and strength, active studies and developments have been conducted for organic-inorganic nanocomposite materials in which an inorganic particle material is blended in resin, and various manufacturing methods thereof have been proposed. A typical one thereof is a composite material described in the Japanese Patent Examined Publication No. H7-47644. This publication shows a method to obtain a composite of nylon and the filler, in which montmorillonite is used as an inorganic filler of the resin and caprolactam as a raw material of nylon is impregnated between montmorillonite layers to be polymerized. With this method, mechanical properties of the composite, for example, strength, elastic modulus, surface hardness, and heat resistance were improved, but applications thereof were limited due to the insufficient transparency, hydroscopic property, and surface hardness thereof.
The Japanese Patent Unexamined Publication No. H8-73723 discloses a resin composition including polycarbonate (PC) with a rare-earth element blended. This resin composition was more effective than polycarbonate alone in terms of the transparency, but did not increase in strength, elastic modulus, surface hardness, and heat resistance.
On the other hand, the Japanese Patent Unexamined Publication No. H11-343349 discloses a resin window which achieves an increase in rigidity, strength, and the like as well as an increase in transparency. This resin window is composed of a transparent resin composition which includes a transparent amorphous organic polymer and fine silica particles blended therein, the silica particles having a diameter of not more than wavelength of visible light. The resin composition maintains transparency and increases in strength, elastic modulus, impact resistance, and the like to some extent. However, the silica particles do not adequately reinforce the resin composition because the aspect ratio thereof is 1.
The Japanese Patent Unexamined Publication No. H7-102112 discloses a resin composition using carbon nanotubes as an additive having a diameter of not more than the wavelength of visible light and a high aspect ratio to increase the reinforcing effect. However, the resin is colored black with a few percent of the additive, causing a problem of disfigurement.
Furthermore, alumina and boehmite particles are used as the filler. The Japanese Patent Unexamined Publication No. 2003-54941 discloses a resin composition obtained by melting and kneading needle-shaped boehmite and alumina particles with a long axis length of 1 to 10 μm and an aspect ratio of 40 to 70. However, the fillers have particle sizes considerably exceeding the wavelength of visible light, and the filler particles are not adequately dispersed in the resin, so that the resin composition is not transparent.